In certain vehicles, especially trucks, the driver, and passengers if any, are subjected to a great deal of vibration and road shock during travel in the vehicle. Prior art seat cushions have, in general, been inadequate to provide relief from this discomfort. Most seat cushions or seats known to the applicant have involved air inflated cells or cavities, wherein the shape of the cavities themselves provide support for any existing seat back portion. Only one prior art seat cushion is known to the applicant which includes a water filled cavity, and further, a water filled cavity designed to be only partially filled with fluid. This structure, however, does not disclose any seat back portion designed to be fluid filled, nor means for supporting such a seat back. Thus, no prior art seat cushion is known to the applicant wherein a plurality of fluid filled cavities are included, with an upper cavity designed to be only partially filled with water, this upper cavity further including precisely spaced seams defining secondary cavities thereby. In addition, no fluid filled seat cushion is known including means for retaining said cushion against the seat back, such that the seat cushion can be used in a vehicle or the like.